There may be instances when an AIS-based event that had previously been displayed in Skylight is no longer visible. As a near real-time system, Skylight displays the most up-to-date information available at the time. However, as additional updated AIS data is received or information processes are run, Skylight may learn that the event did not ultimately meet the requirements. In these rare instances, the event is removed from Skylight.
Out of Order AIS messages
One common reason an event is removed from Skylight is additional AIS data is received out of order and Skylight ‘learns’ the event did not actually meet the requirements. Although rare for most events, because of the nature of Potential Dark Activities, it is more likely that additional AIS data will come in out of order and change these events.
In the greatly simplified example below, we can see how this might happen. There are four AIS position messages in the below diagram:
Message 1 was received at 10:15:00 and indicates the vessel’s location at 10:00
Message 2 was received at 11:19:00 and indicates the vessel’s position at 11:14
At 17:14 Skylight would generate a Potential Dark Activity since 6 hours had elapsed with no AIS update to the location information in Message 2.
Message 3 arrives at 20:35:00 with the vessel’s location at 20:30. The Potential Dark Activity event ends and the duration is calculated to be 9h 16m.
Message 4 arrives at 23:45:00 with new information about the vessel’s location at 16:20. With this new, updated information Skylight learns that the vessel was not dark for 9h 16m as originally calculated. Instead, the vessel was dark for only 5h 6m which does not meet the threshold for a Potential Dark Activity. In this case, Skylight will remove the event.
Vessel(s) involved in an event and later classified as a buoy
Skylight is designed to show events involving vessels. For example, a Standard Rendezvous shows where two vessels, transmitting AIS, have traveled in proximity at approximately the same speed. To avoid showing instances where gear that is transmitting AIS is involved in a Standard Rendezvous with its vessel, Skylight runs a daily process to identify and classify buoys.
Skylight has a machine learning model that is run once daily to identify vessels that are actually buoys and re-classify them. If that former vessel was involved in an event before the buoy service ran, then an event would display in Skylight:
The above event was viewed in Skylight on approximately 2022-10-27 T18:35:00 GMT which is before the buoy service was run for the day. Once the buoy service was run, the above vessels were correctly classified as ‘buoys’ and the event removed from Skylight.
A vessel that has been classified as a buoy will be viewable in the Vessel Details Screen, but there will be no events associated with the vessel after the buoy service is run.
